This specification relates to controlling electrical loads.
Lighting control within buildings is traditionally limited to control of lights in the ceiling that illuminate a general area. This type of control is typically referred to as ambient lighting control. More recent advances in energy-efficient lighting design have seen a shift in philosophy towards reducing the ambient light and compensating for the illumination reduction with lighting on the desk or work plane. The desk or work plane is referred to as a task area, and the illumination of the task area is referred to as task lighting. Less area illumination is typically needed for ambient light, as it is used to simply light an area, ensure that there is sufficient lighting for walkways and for safety purposes, etc. Task lighting is typically used for reading and other work activity, and thus the required illumination within the task area is typically higher than the illumination of the general area of which the task area is a sub-portion. This combination of reducing ambient lighting and providing sufficient task lighting can increase energy efficiency and lower overall power consumption.
When a person is not at the task area, there is no need to provide task-level lighting. Occupancy sensors that sense occupancy in the general area can be used to automatically turn task lamps off based on lack of occupancy, along with plug loads based on lack of occupancy. However, as a general area may often include several or more separate task areas, such as in the case of multiple work stations in a laboratory or multiple cubicles in an office setting, the sensing of a physical stimulus in one task area of the general area may result in unnecessary ambient illumination and power being provided to one or more unoccupied task areas.
Another cost-savings measure is the use of daylighting. Daylighting works by introducing a photocell sensor, usually placed in the ceiling to measure illumination level in a general area, and automatically adjusting the light output from ambient light sources based on the measured illumination levels. Daylighting, however, does not accurately control the light level in the task areas.